Summary of Work: Linkage analyses are being conducted in three large pedigrees, designated LMG2, MSUDF1 and HOLON, which segregate for dominant nonsyndromal hearing impairment. The probands from these pedigrees, as well as those from nine pedigrees segregating autosomal recessive hearing impairment and determined to be too small for meaningful linkage analyses, are also being screened for mutations in known DFN genes (GJB2 = DFNA3/DFNB1; Myosin VIIB = DFNB2) and several K-channel genes that are candidates for DFN genes by virtue of their map positions. Linkage analyses have excluded the known DFN loci in MSUDF1 and LMG2. Efforts are underway to extend the MSUDF1 pedigree by ascertaining a portion of a family situated in England. Genome wide screens for MSUDF1 and LMG2 are now being conducted. Linkage to markers near DFNA1 was detected in the HOLON pedigree (max LOD = 3.7; theta = 0.16). However, the obligate DFNA1 region is excluded on the basis of several recombinations. Additional clinical data is being collected to help evaluate the possibility that phenocopies and non-penetrance are contributing to apparent recombinations with DFNA1. It is possible that this family defines a new DFN locus on 5q31. Mutations in the GJB2 gene have been identified in the probands from three of the nine recessive hearing impairment pedigrees. We are in the process of confirming these findings in the probands and evaluating the rest of the families for the presence of these putative mutant alleles. As a collaboration with Dr. Bronya Keats, orthodox Jewish families with likely recessive nonsyndromic hearing impairment are being ascertained in Baltimore, New Jersey, New York and Toronto. The goal is to identify the gene(s) associated with hereditary hearing impairment in this population.